But the software giant from Seattle is making a determined effort to unseat the current champion.
It became the first of the console giants to release a next-generation system with its Xbox 360.
It aims to have sold more than five million units by the end of June and is hoping to hit 10 million before the PS3 launch.
In an interview with the BBC News website on Wednesday, Sony's head of worldwide studios Phil Harrison shrugged off its rival's prediction, saying he doubted it would achieve the target.
The comments have promoted a swift response from Microsoft, with corporate vice president Peter Moore challenging Sony's PS3 predictions.
"I'll throw back at him that I doubt he can deliver six million units from November to March. I don't think it is going to happen," he said.
"The question you have is 'will they be able to meet the demand?'
"We have learnt that driving demand is fine if you have huge amounts of supply to meet that. It is not easy to do," he said.
Mr Moore is talking from experience. Microsoft suffered huge problems in manufacturing enough Xbox 360s to meet demand when the system was launched last year.
Two for one
When the PS3 arrives in November, a year after the Xbox 360, it will sell for $499 in the US.
A premium model will cost $599 compared with $399 for the high-end model from Microsoft, though the PS3 includes a superior-capacity Blu-ray DVD drive.
However, Microsoft has even suggested the price differential could work in its favour.
Mr Moore said gamers tended to buy two gaming systems, so they would be able to buy a 360 and a Wii for the price of a PS3.
"Xbox 360 is going to be the only place you can play Halo 3 and Grand Theft Auto IV on the same platform.
"And you combine that with what Nintendo is doing, at what we think is going to be a pretty competitive price point, that is a compelling package."
Japanese troubles
Despite its head start, Microsoft still has to make a significant dent in Sony's home ground.
The Xbox 360 received a lukewarm response in Japan when it launched there, selling 100,000 units.
Japan is a key area for the three console makers, as it is one of the biggest markets for video games.
Microsoft is trying to woo Japanese gamers with titles specifically designed for them, such as the role-playing games Blue Dragon and Lost Odyssey.
Alfred.Hermida-INTERNET@bbc.co.uk
